1. Field of the Invention
The present invention, called the Heart State Analyzer (HSA), relates to medical instruments and more particularly to the detection and analysis of human heart beat waves by a non-invasive EKG (electrocardiograph or "ECG") system and method.
2. Description of the Related Art
In the human heart a wave of depolarization is initiated by a spontaneous electrical impulse in a local region at the top of the heart, called the sinoatrial node or pacemaker. That depolarization wave causes a contraction of the heart muscle, as it moves down the heart, and causes pumping of the blood. The ordered contraction of the heart muscle depends upon the integrity of the electrical conduction system (including the "His-Purhinge" fibers) and an adequate supply of blood to the heart from a small number of major coronary arteries, which are the blood vessels leading to the heart. The failure of the heart to receive an adequate supply of blood ("ischemia") may result in the symptoms of angina pectoris, myocardial infarction and even death. Although the present invention is described as being useful in connection with the early detection of silent ischemia, and ischemia in general, it will be understood that further research using the Heart State Analyzer will disclose other heart diseases and abnormalities that it may detect or analyze. Heart disease is the leading cause of death in men in the United States over thirty years of age.
A type of coronary artery disease, in which there are periods when the heart does not receive a sufficient blood supply ("myocardial ischemia") is a major cause of heart attacks. It causes injury or death to large numbers of persons without prior symptoms of heart disease, such as prior attacks of angina pectoris, myocardial infarction, or abnormal finding on the conventional EKG.
The most common cause of a heart attack is that one or more of the major coronary arteries to the heart is suddenly blocked. Such sudden blockage generally occurs in a patient affected with "coronary atherosclerosis", a narrowing of the arteries due to "plaque", which is an accumulation of excess cellular and connective tissue and cholesterol. Such blockage may be sudden and catastrophic, for example, because of a spasm or because a blood clot blocks the restricted artery. A second cause of heart attack is the gradual occlusion of the opening (lumen) of the artery by plaque deposits, i.e., "stenosis" of one or more coronary arteries.
One conventional non-invasive method of determining the presence of heart disease is, in effect, to provoke certain of its symptoms, such as angina pain or abnormal EKG signs by a "stress test" in which the patient walks rapidly on a treadmill. The stress test is controversial and inconclusive. In a certain number of cases it causes heart attacks and, in addition, some patients who pass the stress test without displaying chest pain or EKG abnormalities nevertheless prove to have heart disease.
Another non-invasive method of diagnosis utilizes "PET" (positronemission tomograph) images. A cross-sectional image of regional metabolism is displayed in a color-coded CRT representing the gamma radiation given off in the collison of electrons in cell with positrons emitted by radionuclides incorporated into metabolic substances. However, such imagery is expensive, time consuming, is not generally availble and may be difficult to interpret.
Various types of devices are commercially available, or have been suggested in the patent or medical literature, for the monitoring of EKG signals.
U.S. Pat. No. 4,679,144 to Cox et al relates to a programmable apparatus worn by a patient during the day and performing continuous real-time analysis of EKG signals. It uses the conventional placement of leads.
Other patents and articles cited in the Cox et al patent relate to other computer-based EKG systems. In U.S. Pat. No. 4,193,333 to Schlager, which utilizes twelve leads, the "R" wave peak of each heart beat is detected and initiates the timing. Digital memory addresses are assigned as 256 time segments to components of the EKG wave, which are compared to preset references.
In "body surface mapping", a large number of unipolar EKG leads, for example 87, are attached to the patient's body using a body surface potential mapping system (e.g., Model HMPM-51005 of Chunchi Denish Co., Japan), see Ikeda et al, "Detection of Posterior Myocardial Infarction By Body Surface Electrocardiographic Mapping After Dipyridamole Infusion", J. Electrocardiology 19(3), 1986, 213-224. The map displayed by such systems is not the result of a mathematical or statistical analysis of the data. Interpolation is subjective, and the map may be difficult to interpret.
A series of articles authored by Robert L. Lux and others of the College of Medicine, University of Utah, relate to isopotential maps using a large number of ECG leads. The articles Lux et al, "Redundancy" I "Spatial compression" and II "Temporal compression" Cir. Res. 49, 186 and 197 (1981) explain that the 192 leads (body surface electrocardiograms) may be reduced to 12 coefficient waveforms, a data compression of 16:1. Further, the data may be compressed 20:1 using "K-L" expansion. The system provides QRST maps of individual subjects characterized by 216 numbers (coefficients), see Green, Lux et al, "Detection and localization of coronary artery disease with body surface mapping in patients with normal electrocardiograms", Circulation 76, No. 6, 1290-1297 (1987--non-prior art).